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Biomedical subjects

John Chambers

Publications and source records attributed to John Chambers.

33 records · Page 2Linked to original sources
PubMed2004

Maternal cardiac function during pregnancy at high altitude.

OBJECTIVE: To investigate the maternal cardiovascular adaptation in pregnancy at high altitude, compared with that at sea level. DESIGN: Cross sectional study. SETTING: Two maternity units providing routine antenatal care: one at 4370 m above sea level (Cerro de Pasco, Peru) and one at sea level (Lima, Peru). POPULATION: We examined 175 pregnant women at 5-41 weeks of gestation and 16 non-pregnant controls resident at high altitude and 132 pregnant women and 18 non-pregnant controls at sea level. METHODS: Two-dimensional and M-mode echocardiography of the left ventricle. MAIN OUTCOME MEASURES: Maternal cardiac output and left ventricular longitudinal and transverse systolic function indices. RESULTS: Pregnancy at high altitude, compared with sea level, is associated with 11% lower birthweight and 31% lower maternal cardiac output, due to 15% lower stroke volume and 11% lower heart rate. The lower stroke volume was due to a lower preload and impaired longitudinal and transverse left ventricular systolic function. Mean arterial pressure was about 8% lower during pregnancy at high altitude versus sea level. Pregnant women at high altitude failed to expand their intravascular space to the same extent as the sea level group: cardiac output increased by 17%, left atrial diameter by 12% and end-diastolic diameter by 1% at high altitude versus 41%, 25% and 5%, respectively, at sea level. CONCLUSIONS: Pregnancy at high altitude, compared with sea level, is characterised by lower cardiac output due to lower heart rate and lower stroke volume and reduced expansion of the maternal intravascular space compared with the non-pregnant state.

Adaptation, Physiological↗
PubMed2004

Hemodynamic performance on exercise: comparison of a stentless and stented biological aortic valve replacement.

BACKGROUND AND AIM OF THE STUDY: Although stentless valves are expected to be hemodynamically superior to stented valves, the results of comparative trials have been inconsistent. The study aim was to compare hemodynamic function at rest and on exercise in 50 stentless and stented biological replacement aortic valves METHODS: Twenty-one patients with a Toronto stentless porcine valve and 29 with a Perimount stented bovine pericardial valve were exercised using a bicycle ergometer. Echocardiography was performed before, and during exercise testing. RESULTS: Patients with either valve type were exercised to a similar degree. Transaortic resistance was slightly lower in the Perimount compared with the Toronto at rest (p = 0.03) and at peak exercise (p = 0.04), and flow was higher in the Perimount at rest (p = 0.007), but not at peak exercise. There were no significant differences between the valve types in peak velocity, mean pressure difference or effective orifice area either at rest or on peak exercise. CONCLUSION: There were no clinically significant differences in hemodynamic function between the stented and stentless biological valves chosen for comparison either at rest or during bicycle exercise.

Aged↗
PubMed2004

Determinants of left ventricular mass in aortic stenosis.

BACKGROUND AND AIM OF THE STUDY: There are many possible determinants of left ventricular (LV) mass, including the angiotensin-converting enzyme (ACE) genotype, which have rarely been compared in aortic stenosis (AS). The study aim was to investigate these determinants in patients with all grades of AS. METHODS: Transthoracic echocardiography and an analysis of ACE genotype was performed in 91 patients with aortic valve thickening and a peak aortic velocity >2.0 m/s. RESULTS: Univariate relationships were identified between LV mass index and effective orifice area (R = 0.22), and peak transaortic pressure difference (R = 0.36). LV mass index was similar for the ACE-II (152+/-37 g/m2), ACE-ID (145+/-46 g/m2) and ACE-DD (161+/-56 g/m2) genotypes. LV mass index was significantly greater in males (162+/-52 gm/m2) than in females (137+/-38 gm/m2; p = 0.014). The multivariate determinants varied according to the grade of AS: diastolic blood pressure (p = 0.028) in mild stenosis; peak transaortic pressure difference (p = 0.03) in moderate stenosis; and peak transaortic pressure difference (p <0.0001) and gender (p = 0.02) in severe stenosis. LV hypertrophy was present in 15 of 24 patients (63%) with mild AS, in 21 of 27 (78%) with moderate AS, and 32 of 40 (80%) with severe AS. CONCLUSION: LV hypertrophy is common, even in mild AS, when it is independently related only to the systemic blood pressure. This suggests that antihypertensive agents should be considered early in the natural history of AS.

Aged↗
PubMed2003

Low Gradient, Low Ejection Fraction Aortic Stenosis.

Low gradient aortic stenosis can be caused by critical aortic stenosis causing left ventricular impairment or by more moderate aortic stenosis coexisting with another cause of left ventricular impairment. The main challenges are to differentiate these two states and then to determine whether the left ventricle is likely to recover after aortic valve surgery. Exhaustive echocardiography is necessary, including the use of dobutamine stress. Guideline criteria for severe aortic stenosis are given in this article. The most secure criteria are mean transaortic pressure difference greater than 30 mm Hg and effective orifice area less than 1.2 cm(2) during dobutamine stress. However, the presence of left ventricular contractile reserve more closely determines outcome after surgery than do markers of stenosis. Surgery is most clearly indicated if there is severe aortic stenosis and an increase in the systolic velocity integral by greater than 20% during dobutamine infusion. Preoperative catheterization is necessary to determine coronary anatomy, but the aortic valve should not be crossed because of the relatively high risk of death, stroke, pulmonary edema, and cardiogenic shock. In patients judged too ill for immediate surgery, a period of medical resuscitation with diuretics and dobutamine should be considered. Balloon valvotomy is not indicated.

Journal Article↗
PubMed2003

Maternal cardiac function in twin pregnancy.

OBJECTIVE: To investigate maternal cardiac function in twin pregnancy. METHODS: We conducted a cross-sectional study of 119 pregnant women with twin pregnancies at 10-40 weeks' gestation. Two-dimensional and M-mode echocardiography of the left ventricle was performed in the left lateral decubitus position to assess left ventricular longitudinal and transverse systolic function. The measurements were compared with those obtained from 128 women with singleton pregnancies previously reported. RESULTS: In twin pregnancies, compared with singletons, maternal cardiac output was greater by 20% (P <.001), because of a greater stroke volume (15%, P <.001) and heart rate (3.5%; P =.04). Furthermore, in women with twins there were greater left ventricular end-diastolic and left ventricular end-systolic dimensions, left ventricular mass (13.5%; P <.001), fractional shortening (3%; P =.04), and ejection fraction (2.5%; P =.04). Mean arterial pressure and global time to shortening in women with twins, compared with singletons, were less in the first trimester by approximately 2%, but after midpregnancy they increased progressively, so that at term the measurements were greater by 3% and 5.7%, respectively (P =.03). Conversely, long axis shortening in women with twins, compared with singletons, was greater in the first trimester by approximately 6.5%, but at term it was 3% less (P =.01). Twin pregnancies that subsequently developed preeclampsia had a hemodynamic profile similar to the rest of the twin population. CONCLUSION: Twin pregnancy is characterized by an even more hyperdynamic circulation than singleton pregnancy. Left ventricle longitudinal systolic function and mean arterial pressure are more abruptly affected after 20 weeks compared with singleton pregnancies.

Adult↗
PubMed2003

Determinants of symptoms and exercise capacity in aortic stenosis: a comparison of resting haemodynamics and valve compliance during dobutamine stress.

AIMS: Valve compliance might determine the onset of symptoms better than resting measures of aortic stenosis. This study compared valve compliance measured by dobutamine stress echocardiography with resting haemodynamic variables against the end-point of symptoms at low workload during exercise testing. METHODS AND RESULTS: Echocardiography was performed at rest and during each stage of a dobutamine stress test in 65 asymptomatic patients with moderate or severe aortic stenosis. Each patient also completed a modified Bruce treadmill exercise test. During dobutamine stress, peak transaortic velocity increased by 1.0 (0.4) m/s and effective orifice area by 0.25 (0.22) cm(2). Valve compliance was 0.23 (0.10) cm(2)/100ml.s(-1), and was independent of baseline effective orifice area. In the 19 patients limited by symptoms on exercise testing, valve compliance was significantly lower (0.19 (0.09) cm(2)/100ml.s(-1)) than in those who remained asymptomatic (0.25 (0.10) cm(2)/100ml.s(-1), p=0.03). Effective orifice area at peak stress was also lower (1.0 (0.3) vs 1.2 (0.4) cm(2), p=0.03), but there were no significant differences in resting measures of effective orifice area, transaortic velocity, or mean pressure drop. CONCLUSIONS: Effective orifice area is flow-dependent in patients with moderate and severe aortic stenosis with preserved left ventricular function. Exertional symptoms are better predicted by compliance than resting effective orifice area, mean pressure drop or peak transaortic velocity.

Adult↗
PubMed2003

Infective endocarditis in dialysis patients: new challenges and old.

BACKGROUND: Since the 1960s chronic hemodialysis (HD) has been recognized as a risk factor for the development of infective endocarditis (IE). Historically, it has been particularly associated with vascular access via dual lumen catheters. We wished to examine the risk factors for, and consequences of, IE in the modern dialysis era. METHODS: Cases of IE (using the Duke criteria) at St. Thomas' Hospital (1980 to 1995), Guy's (1995 to 2002), and King's College Hospitals (1996 to 2002) were reviewed. RESULTS: Twenty-eight patients were identified as having developed IE (30 episodes of IE). Twenty-seven patients were on long-term HD and one patient was on peritoneal dialysis (PD). Mean age was 54.1 years, and mean duration of HD prior to IE was 46.3 months. Eight patients were diabetic. Primary HD hemoaccess was an arteriovenous fistula (AVF) in 41.3%, a dual-lumen tunneled catheter (DLTC) in 37.9%, a polytetrafluoroethylene (PTFE) graft in 10.3%, and a dual- lumen non-tunneled catheter (DLNTC) in 4%. The presumed source of sepsis was directly related to hemoaccess in 25 HD patients: DLTC in 48%; AVF in 32%; PTFE in 12%; and DLNTC in 4%. Staphylococcus aureus[including methicillin resistant Staphylococcus aureus (MRSA)] was present in 63.3%. The mitral valve was affected in 41.4% of patients, aortic valve in 37.9% of patients, and both valves were affected in 17.2% of patients. Of note, 51.7% of patients had an abnormal valve before the episode of IE. In 15 cases surgery was undertaken. Fourteen patients survived to discharge, and 12 survived for 30 days. In 15 cases antibiotic treatment alone was employed; in this case, eight patients died and seven survived to discharge. CONCLUSION: This is the largest reported confirmed IE series in dialysis patients. Infective endocarditis in HD patients remains a challenging problem-although hemoaccess via dual-lumen catheters remains a significant risk, many cases developed in patients with AVFs and this group suffered the greatest mortality. An abnormal valve (frequently calcified) was another risk factor; because valve calcification is now common after 5 years on dialysis, more effort in preventing this avoidable form of ectopic calcification may reduce the risk of developing IE.

Adult↗